a) Field of the Invention
The invention relates to a method for the production of a steering spindle portion forming a section of a steering spindle, which, at least in an end region, includes a reinforcement section over which the steering spindle portion has a wall thickness that is increased compared to a section of the steering spindle portion adjoining toward the longitudinal center of the steering spindle portion. The steering spindle portion comprises a tube and a sleeve located in the reinforcement section of the steering spindle portion and forming the increased wall thickness. The method comprises the formation of connection elements which serve for the connection of the steering spindle portion with a steering wheel or a yoke for a universal joint or a steering pinion and of which at least a portion is located in the reinforcement section reinforced by the sleeve. The invention further relates to a steering spindle portion implemented in this manner and connected with a steering wheel.
b) Description of Related Prior Art
Steering spindles of motor vehicles conventionally comprise several steering spindle portions each forming a section of the steering spindle. On the steering spindle section which, relative to the traveling direction, is the rearmost, the steering wheel is secured in position on its rearward end. On the steering spindle section which, relative to the traveling direction is the frontmost, a pinion for the engagement into the steering gear is frequently secured in position at its front end. Apart from steering spindle portions connected across universal joints with one another, steering spindle portions that are displaceable (telescopable) with respect to one another can be provided, which serve for setting the length of the steering column and/or for receiving longitudinal dislocations in the event of a crash.
In a known embodiment, the connection of the steering wheel with the rearmost steering spindle portion takes place by means of a bolted connection. The steering spindle portion realized in the form of a hollow shaft includes for this purpose a connection section at the end side which, starting from the end of the steering spindle portion, comprises a substantially hollow cylindrical section and adjoining this a conical section expanding toward the center of the steering spindle portion. The hollow cylindrical section is provided with internal threading and outer toothing. The outer toothing engages into an inner toothing of the hub of the steering wheel and by means of the inner threading the steering wheel is bolted to the steering spindle portion. For this purpose, the steering spindle portion must have a sufficiently large wall thickness in the connection section, in particular in the hollow cylindrical end section. This thickness is greater than the wall thickness required for the transmission of the torque over the remaining length of the steering spindle portion. For the implementation of the steering spindle portion conventionally tubes are therefore utilized which—apart from the connection section—initially have a greater wall thickness than is required. The tube is subsequently worked over its entire length, in particular by swaging or similar reforming methods, for example, knead-working. Herein the diameter in the connection section of the tube is decreased. Over the remaining length of the tube, the wall thickness of the tube is decreased. Further, herein structures can also be worked in over sections of the tube which, for example, serve for the telescopable yet non-turnable connection with a further steering spindle portion. The realization of such contours, in particular in the form of spiral toothings or cloverleaf profiles, is known. For example DE 197 50 005 C1 discloses a steering spindle portion with such contours.
This process is highly labor intensive and also difficult to control due to the required reforming of the tube over its entire length.
While it is feasible to thicken up the wall thickness of a tube by swaging, however, due to factors limiting such thickening, a tube must nevertheless be utilized as a starting product which has a greater wall thickness than would be necessary for the requisite torque transmission. The steering spindle portion becomes thereby overall heavy or the tube must, again, be worked over its entire length in order to decrease accordingly the wall thickness apart from the connection section.
DE 10 2004 009 188 A1 discloses two telescopably connected steering spindle parts which, viewed in longitudinal cross-section, have complicated contours with different thickness regions of their wall thicknesses, wherein at their ends remote from one another connection sections are provided for the connection with a steering wheel or a steering gear. Such wall thickness profiles can be realized through reforming working of tubes over their entire lengths.
Securement in position of a steering wheel on a steering shaft by means of a bolt located transversely to the axis of the steering spindle, which bolt cooperates with a retaining cone and displaces it in a recess of the steering wheel hub and tightens it against the steering shaft, is disclosed in EP 1 138 575 B1. The steering spindle portion, on the end of which the steering wheel is secured, is solid. However, the steering spindle portion could also be realized as a hollow shaft with a sufficiently thick wall thickness.
A further securement of a steering wheel at the end of the steering spindle portion adjoining the steering wheel is disclosed in U.S. Pat. No. 4,819,961 A. The steering spindle portion realized as a hollow shaft includes at the end side a connection section in which the tube of the steering spindle portion initially tapers conically toward its end and adjoining thereon includes a hollow cylindrical section with an inner toothing. In the connection section is disposed a clamp piece whose outer contour corresponds to the inner contour of the tube and which projects at the end side from the tube. It comprises first and second outer toothings which, on the one hand, cooperate with the inner toothing of the tube and, on the other hand, with an inner toothing of the steering wheel hub, and comprises further an inner threading into which a bolt engaging on the steering wheel hub is screwed in order to tighten the parts with one another. Due to the solid tightener set into the connection section, the wall thickness of the steering spindle portion can be implemented such that it is constant over its length. With such a clamping connection, there is the risk that the applied clamping forces decrease over time whereby an undesirable play can develop. Moreover, the clamp piece must be introduced from the steering wheel-remote side through the steering spindle portion. The steering spindle portion consequently cannot include any regions with decreased cross-section, for example in order to implement a telescopable, torque transmitting connection with a further steering spindle portion. The clamp piece furthermore can slip into the interior of the steering spindle portion if the steering wheel is removed and is subsequently inaccessible.
DE 25 45 927 B2 discloses a steering spindle portion in the form of a safety shaft piece. This safety shaft piece comprises a corrugated central section extending over the major portion of the length of the shaft piece and adjoining which is a cylinder sleeve section on both sides. In the cylinder sleeve section is disposed a cylindrical pin of a shaft connection. Into the cylindrical pin of the shaft connection several radial bores are worked, whereupon the shaft tube with its end-side cylinder sleeve section is axially slid onto the pin. From the material of the cylinder sleeve section subsequently radial projections are pressed out and pressed into the radial bores, whereupon the pin and the cylinder sleeve section are additionally connected with one another on the axial front side facing away from the shaft tube by welding.
DE 103 47 101 A1 discloses in general the connection of two tubular structural parts by means of external high-pressure reforming. The description explains that in this reforming the external tube is plastically deformed and the internal tube is elastically deformed.
U.S. Pat. No. 4,304,147 discloses a steering column in which, for the reinforcement of an upper section of the steering column, an inner tube is disposed in the outer tube to increase the wall thickness. For the securement of the inner tube in the outer tube, the outer tube is brought into contact with the inner tube using mechanical means. The inner tube, moreover, includes a tapering portion which is in contact with the outer tube. The two tubes in contact with one another act like one tube with a wall thickness equal to the composite wall thickness of the two utilized tubes as long as the tubes are subjected to flexural stress.
However, in this case, the structure proposed in U.S. Pat. No. 4,304,147 no longer provides the desired reinforcement effect if, in addition to flexural stress, also tensile and pressure stresses, securement stresses or torques are to be absorbed by the tube-in-tube combination.
WO 97/48507 A1 discloses the connection of two tubular shaft parts, for example of a steering spindle, in an overlapping section of the two shaft parts, wherein the shaft portion located interiorly in the overlap section is expanded.
WO 02/02377 A1 shows an overload safety, in particular for a steering wheel lock, wherein an outer sleeve-shaped joining portion encompasses a tubular steering spindle portion and is connected with it via a press-fit, wherein the friction closure is released in the event of an overload.
U.S. Pat. No. 4,469,356 A relates to the implementation of plugs for fluid lines, in particular in aircraft. For the simple implementation of such plug connectors the plug connectors are formed integrally with the ends of the pipe lines, wherein the ends of the pipe lines are reformed correspondingly together with sleeves disposed thereon.
A steering spindle portion of the type described in the introduction is disclosed in WO 2007/098513 A1. In the production of this steering spindle portion a sleeve is set into, in particular pressed into, an end section of the tube, whereupon the end section of the tube and the sleeve are reformed jointly. Herein, a flowing of the material of the tube and of the sleeve occurs. Further, after the reforming of tube and sleeve, internal threadings are introduced into the inner wall of the sleeve and the tube is provided with an outer toothing in a section adjoining its end. In the steering spindle portion implemented in this manner there is the risk in the case of a repair that the sleeve becomes detached from the tube, in particular if the portion involved is that steering spindle portion at which the steering wheel is connected. The reason therefor is that for the detaching of the steering wheel a hammer is frequently pounded onto the central connection bolt to facilitate detaching the steering wheel from the steering spindle. Through these hammer blows it is possible for the sleeve to be driven into the interior of the tube. A further disadvantage of the solution proposed in this document comprises that the joined reforming of the sleeve with the connection section requires a relatively complex reforming method, for example swaging operations.